1. Field of the Invention
The present invention relates to mangetic recording members, and more particularly, it is concerned with high density magnetic recording members having excellent lubricity and durability.
2. Description of the Prior Art
With magnetic recording members, in particular, video tapes, since the tape runs while contacting a fixed magnetic head, a drum, a guide pole, etc., the tape must have a low coefficient of friction and run smoothly and stably over a long period of time, and at the same time, the tape must have excellent durability since it is vigorously rubbed with a rotary magnetic head.
For this reason, in the past, higher aliphatic acids, higher aliphatic acid esters, paraffin based hydrocarbons, silicone oils, e.g., dimethyl polysiloxane, diphenyl polysiloxane, etc., have been incorporated into a magnetic coating containing a ferro magnetic powder and a binder. In particular, a silicone oil has advantageously been used since the desired effect can be attained by addition of a small amount of the silicone oil.
The above additives are described in Japanese Patent Publication Nos. 18064/1966, 186/1968, 669/1968, 15624/1972, U.S. Pat. Nos. 2,654,681, 3,470,021, 3,497,411, 3,525,694, 3,634,253, etc.
These conventional additives, however, have failed to provide video tapes with sufficient lubricity and durability. Moreover, the additives tend to ooze out on the surface of a magnetic layer, i.e., the so-called "blooming" phenomenon occurs, and thus, blooming, etc., have occurred during the storage of the tapes.
In addition, as organic silicone compounds, those compounds represented by the formula (II) (Japanese Patent Publication No. 14249/1974) ##STR2## wherein R and R' are hydrocarbon groups containing 7 to 26 carbon atoms, and n is an integer of 1 to 20; and the formula (III) (Japanese Patent Application (OPI) No. 32904/1975) ##STR3## wherein R and R' are hydrocarbon groups containing 8 to 18 carbon atoms, R" is hydrogen or methyl, and 15 .gtoreq. m .gtoreq. 1, 16 .gtoreq. (n.sub.1 + n.sub.2) .gtoreq. 2; are known.
The compounds represented by the formula (II) are not desired since durability is not improved, and since their compatibility with binders is low, thus causing the blooming phenomenon to occur. Although the reason for this is not clear, it is believed that the bonding between the hydrocarbon group and silicone is an ether bond having a low polarity.
The compounds represented by the formula (III) have been found undesired in that the kinetic coefficient of friction between the tape and a head drum of a video tape recorder is high under a high load, thus sometimes causing a squeeking. Moreover, a sufficient improvement in durability has not been obtained. Although the reason for this is not clear, it is believed due to the hydrophilic alkyleneoxy chains contained in the molecules.